To: "Joshua D. Drake" <jd@commandprompt.com>
cc: Gregory Stark <stark@enterprisedb.com>,
	Simon Riggs <simon@2ndquadrant.com>,
	Bernd Helmle <mailings@oopsware.de>, mfatticcioni@mbigroup.it,
	pgsql-performance@postgresql.org
Subject: Re: DRBD and Postgres: how to improve the perfomance? 
In-reply-to: <46E2CAAF.50205@commandprompt.com> 
References: <2C070D1C3970467FF64F6B6A@imhotep.credativ.de>
	<1189232904.4281.19.camel@ebony.site>
	<87k5r1zd52.fsf@oxford.xeocode.com>
	<46E2CAAF.50205@commandprompt.com>
Comments: In-reply-to "Joshua D. Drake" <jd@commandprompt.com>
	message dated "Sat, 08 Sep 2007 09:15:43 -0700"
Date: Sat, 08 Sep 2007 12:39:37 -0400
Message-ID: <24337.1189269577@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

"Joshua D. Drake" <jd@commandprompt.com> writes:
> Gregory Stark wrote:
>> "Simon Riggs" <simon@2ndquadrant.com> writes:
>>> You're right, but the distinction is a small one. What are the chances
>>> of losing two independent servers within a few milliseconds of each
>>> other? 
>> 
>> If they're on the same power bus?

> That chance is minuscule or at least should be.

It seems a bit silly to be doing replication to a slave server that has
any common point of failure with the master.

However, it seems like the point here is not so much "can you recover
your data" as what a commit means.  Do you want a commit reported to the
client to mean the data is safely down to disk in both places, or only
one?

			regards, tom lane